Retry when heard: a message that waits for the other station
This post is for anyone who has sent an APRS message, watched it fail, pressed Retry, and watched it fail again. It covers retry when heard, a feature of APRS Connect Pro, and QRX, a free mailbox service that solves the same problem from the receiving end. It goes through why messages fail, what the watch does, the Waiting to be heard list, and how the two relate.
Why a message fails
An APRS message counts as delivered when the other station sends back an acknowledgement. APRS Connect retries on its own: 30 seconds at first, doubling to a five-minute ceiling, six attempts in all, and the last attempt waits the full five minutes before the message is marked Not delivered.
Most failures are not a bad path or a busy channel. When the app hears its own packet come back through a digipeater, it marks the message Digipeated, which is proof it was radiated. A message can be repeated perfectly and still go unanswered, because the other station's radio was off, or they only switch on for a weekly net. A station that is not on the air cannot acknowledge anything.
Why pressing Retry is a guess
A failed message shows a Retry button on the bubble itself, and the thread list flags the conversation. Retry is free and it works. Its weakness is timing: pressing it an hour later is a guess about when the other station is back, and each guess spends a full retry run on a shared channel. What you actually want is an attempt at the moment the station appears.
What retry when heard does
With APRS Connect Pro, a failed message can wait for its station instead. The app watches for that exact callsign and SSID, and the next time it is heard, over the radio or through APRS-IS, the message goes out again with the same retry schedule and the same wire ID, so a late acknowledgement still matches.
The watch is deliberately spread out:
| Event | What happens |
|---|---|
| The station is first heard | Retry cycle 1, the normal six-attempt run |
| Cycle 1 fails | Hold off for one hour |
| Next hearing after the hold-off | Retry cycle 2 |
| Cycle 2 fails | Hold off for eight hours |
| Next hearing after the hold-off | Retry cycle 3 |
| Cycle 3 fails | Final failure, and the notification arrives |
Three tries in all, and the watch lapses two weeks after it was set. The spacing serves both kinds of station: one that only switches on for a weekly net gets one try per visit, and one that beacons every two minutes cannot burn all three tries in one evening. Only the final failure notifies; the first two cycles failing are silent, because you asked for the wait.
One message's watch, from the failure that set it to the third and last cycle, with the hold-offs between hearings.
The match is by exact SSID. Hearing W1ABC-9 says nothing about whether W1ABC-7 is listening, so a message to W1ABC-7 waits for W1ABC-7 and nothing else.
While a watch is on, the bubble carries a line of its own under the delivery status, "Retries when W1ABC-7 is heard · 3 tries left", and the message screen repeats it with the date the watch lapses. The Retry button still works by hand, and Stop waiting in the message's long-press menu ends the watch.
Ask each time, always, or never
Settings → Messages → Retry when heard decides what happens when a message fails:
- Ask each time (the default) puts the question on screen if the app is in hand, and in the failure notification if it is not.
- Always sets the watch without asking.
- Never leaves the failure alone.
The failure notification carries buttons that act without opening the app: Retry now on every failure, Retry when heard when the app is asking, and Stop waiting when a watch was set for you.
Two cases are never watched: a message sent without a message number, which nothing could acknowledge, and a message QRX has already stored for a registered recipient, which QRX will deliver itself. A message whose path says NOGATE or RFONLY listens to the radio alone.
The Waiting to be heard list
Waiting to be heard lists every watched message on one screen. It is reached two ways: a banner at the top of the message list saying how many are waiting, and a Waiting to be heard row in the More menu, which carries the same count and reads "no messages waiting for a station" when there are none.
Each row names the message, the station it is waiting for, how many tries are left, and the date the watch lapses. A row inside one of the hold-off periods says when the next try becomes possible, and one being retried at that moment says so. Tapping a row opens the message itself; Stop waiting on the row ends that watch without opening anything.
QRX: the same problem from the receiving end
Retry when heard is the sender's answer. QRX is the recipient's. QRX is a missed-message mailbox run by N0JLF: it watches APRS-IS for messages addressed to registered stations and holds whatever goes unacknowledged. Register once, and messages sent while you are off the air are stored, and QRX reminds you on your next beacon that they are waiting. Registration is by base callsign, so it covers every SSID you use.
In APRS Connect, QRX has its own screen on the Services tab. It shows whether you are registered and how many messages are waiting, and pulls them down. Pulled messages arrive from their original senders, so each lands in its own conversation rather than a separate inbox.
The two do not overlap. Retry when heard runs on your phone, for messages you send, needs nothing from the other station, and hears stations over the radio as well as APRS-IS. QRX runs on a server, for messages sent to you, needs you registered beforehand, and sees only what reaches APRS-IS. When both apply to one message, the app leaves delivery to QRX.
Retry when heard is a Pro feature. The Retry button, the six-attempt run and every delivery state are free; Pro adds the watch and the Waiting to be heard screen. QRX, like every service screen, is free.
Where to read more
- Messaging, including the Retry when heard and Waiting to be heard sections.
- APRS services, for QRX and the rest of the Services tab.
- Free and Pro, for the full list of what Pro adds.
Retry when heard needs APRS Connect Pro; the manual Retry button and QRX do not.
